1. Field of Invention
The present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle which can improve safety and reliability as a consequence that the automatic transmission can be operated normally using hydraulic pressure of a low-pressure hydraulic pump when a high-pressure hydraulic pump is stopped.
2. Description of Related Art
Recently, vehicle makers direct all their strength to improving fuel economy due to worldwide high oil prices and strengthening of exhaust gas regulations.
Improvement of fuel economy may be achieved by improving power delivery efficiency in an automatic transmission, and improvement of the power delivery efficiency may be achieved by minimizing unnecessary power consumption of a hydraulic pump.
A recent automatic transmission is provided with a low-pressure hydraulic pump and a high-pressure hydraulic pump so as to improve fuel economy. Therefore, hydraulic pressure generated by the low-pressure hydraulic pump is supplied to a low pressure portion (i.e., a torque converter, a cooling device, and a lubrication device), and hydraulic pressure generated by the high-pressure hydraulic pump is supplied to a high pressure portion (i.e., friction members selectively operated when shifting).
In further detail, general hydraulic pressure of the automatic transmission is generated for the low pressure portion (i.e., generated by the low-pressure hydraulic pump), and hydraulic pressure demanded by the high pressure portion is generated by the high-pressure hydraulic pump and then is supplied to the high pressure portion.
Since power consumption for driving the hydraulic pumps can be minimized, fuel economy may be enhanced. In addition, since a load applied to the hydraulic pumps is reduced, noise and vibration may be reduced and durability may be improved.
Since hydraulic pressure generated by the low-pressure hydraulic pump is supplied to the high-pressure hydraulic pump and the high hydraulic pressure is generated by the high-pressure hydraulic pump according to a conventional hydraulic pressure supply system, the hydraulic pressure supplied to the high pressure portion is insufficient and vehicle cannot drive if the high-pressure hydraulic pump is out of order.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.